1. Field of the Invention
The present invention relates generally to vascular patches used to close an incision in a blood vessel, and more particularly, to a prosthetic vascular patch using an expanded, porous polytetrafluroethylene (PTFE) base layer having an outer elastomeric coating to reduce suture hole bleeding; the present invention also relates to methods for manufacturing such vascular patches.
2. Description of the Prior Art
A number of surgical operations require that an incision be formed in the wall of a blood vessel. Such surgical operations include thrombectomies, endarterectomies, and aneurysmal repair procedures. Carotid endarterectomy is believed to be the most common vascular procedure performed today in the United States. Other surgical procedures which often require that incisions be formed in the wall of a blood vessel include inter-aortic balloon pump procedures, laser procedures, and operations to remove anastomotic hyperplasia.
Currently, there are three techniques used to close the incision in a blood vessel following the completion of one of the above-listed surgical operations. One of these closure techniques is known as a primary closure or simple closure, wherein the incision in the blood vessel is sewn together without the use of a patch. A second technique used to close the incision in a blood vessel uses a section from another vessel, such as a portion of the saphenous vein, as a patch over the incision. The third technique uses a prosthetic material as a patch for closing the wound. The use of a blood vessel patch in conjunction with carotid endarterectomy procedures is generally described by Imparato, Journal of Vascular Surgery, Volume b 7, No. 5, May 1988, pages 715-716.
Regardless of which of the three closure techniques described above is used, a wound is produced in the vessel which typically results in some thickening of the blood vessel wall when the vessel heals. When the primary closure, or simple closure, technique is used to close the incision, the vessel typically has a reduced diameter at the entry site following surgery as compared with the original diameter of the vessel at the entry site. Some studies have reported that the use of the primary closure technique is subject to the problem of recurrent stenosis at the location where surgical intervention was required, possibly due to the narrowing of the vessel accompanied by thickening of the vessel wall at the entry site. By using a patch, the vessel has a greater diameter at the entry site as compared with the use of the primary closure technique, and accordingly, thickening of the vessel wall at the entry site is less significant.
Patches taken from a section of another vessel in the body provide the advantage of widening the vessel at the entry site where surgical intervention was required, while presenting a natural surface to the blood carried by the vessel. A natural, or autogenous, patch, such as a patch formed from a section of the saphenous vein, has a live intimal surface that reduces thrombogenicity; such a natural patch also has a functional vascular system which reduces healing time. However, this technique requires that an additional surgical operation be performed, namely obtaining a section of the saphenous vein. Such saphenous vein patches are typically taken from above the ankle to below the groin regions. Frequently, no acceptable vein for creating a patch is available. In addition, natural patches have been reported to dilate or rupture if the vessel used to make the patch is not sufficiently strong.
The use of a prosthetic patch avoids the disadvantage of performing a second surgical operation to harvest a natural patch from another vessel in the body. Moreover, prosthetic patches have sufficient strength to avoid the dilation and rupturing problems associated with natural patches. The synthetic materials most commonly used to form prosthetic patches are Dacron cloth and PTFE. Dacron-based patches are sufficiently porous that they must first be preclotted with the patient's blood to prevent leakage through the patch following implantation. On the other hand, PTFE patches do not require any preclotting prior to implantation. Moreover, PTFE patches are generally softer and easier to handle than Dacron patches. Moreover, the PTFE surface is less thrombogenic than the preclotted Dacron surface, and PTFE patches have minimal aneurysmal complications as compared with those associated with Dacron patches.
The principal disadvantage of prosthetic PTFE patches, as compared with natural patches or Dacron patches, is the tendency of such PTFE patches to leak blood form the suture holes after the patch is sewn to the wall of the blood vessel. Such suture hole bleeding results in substantial blood loss, a prolongation of the surgical operation time, and occasionally the need for a blood transfusion.
Attempts to diminish bleeding from arterial PTFE patches have included the temporary use of collagen-derived sheets, collagen powders, and oxycellulose compounds applied over the suture line. Hover, no satisfactory decrease in the amount of bleeding has been achieved using these methods. A more effective, though still not satisfactory, manner of sealing the patch suture line is the use of human cryoprecipitate activated with a mixture of a calcium and thrombin. This involves the risk inherent to the administration of blood products from human sources; in addition, this compound is relatively expensive.
Accordingly, it is an object of the present invention to provide a synthetic vascular patch for closing incisions formed din the walls of blood vessels and which minimizes suture hole bleeding associated with current PTFE vascular patches.
It is another object of the present invention to provide such a vascular patch which avoids the requirement for preclotting the patch with the patient's blood.
It is still another object of the present invention to provide such a vascular patch which is biocompatible, which has minimal thrombogenicity, which is physically strong, and which heals relatively quickly.
It is a further object of the present invention to provide such a vascular patch which facilitates the proper and consistent placement of sutures used to secure the vascular patch to the blood vessel in which an incision has been made.
It is a still further object of the present invention to provide such a vascular patch wherein the lumenal surface of the patch that is to be placed against the blood vessel wall is readily discernable from the ablumenal surface of such patch.
It is an additional object of the present invention to provide a method for efficiently and economically manufacturing such blood vessel patches.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.